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The dissociative adsorption of three carboxylic acids (acetic acid, propanoic acid, and acrylic acid), allyl alcohol, and allyl aldehyde on Si(100)2×1 at room temperature has been investigated by X-ray photoelectron spectroscopy (XPS) and temperature programmed desorption (TPD), as well as density-functional theory (DFT) calculations. The C 1s features obtained by XPS measurement for acetic acid, propanoic acid, and acrylic acid show that formation of bidentate carboxylate at a low exposure is followed by that of unidentate carboxylate at a higher exposure, with approximately equal population for both adstructures. The signatures of C 1s features attributed to methyl (285.7 eV), ethyl (285.3 eV), ethenyl (285.0 eV), and bidentate carboxyl (286.8 eV) and unidentate carboxyl (289.8-289.3 eV) carbons were observed for the studied carboxylic acids. The results showed that the carboxyl group is more reactive than the alkyl or alkenyl group towards the Si(100)2×1 surface, with O−H dissociation preferred over [2+2] C=C cycloaddition and the other plausible reaction products. This was also supported by our DFT calculation which showed that the bidentate carboxylate adstructure is the most stable configuration among the calculated adstructures for the aforementioned carboxylic acids. The combined temperature-dependent XPS and TPD studies provided strong evidence for the formation of ketene, acetaldehyde and CO from acetic acid, CO and ethylene from propanoic acid, and CO, ethylene, acetylene, and propene from acrylic acid. Furthermore, the TPD results provided further evidence for the preferred structure of the adsorbate from each of the carboxylic acid on the surface. In addition to carboxyl group, reactivity of the hydroxyl and carbonyl functional groups relative to that of ethenyl group was studied by investigating the reaction of allyl alcohol and allyl aldehyde on Si(100)2×1 at room temperature. The C 1s XPS results supported O−H dissociation for allyl alcohol and [2+2] C=O cycloaddition for allyl aldehyde over the [2+2] C=C cycloaddition. The similarity between the observed C 1s features for allyl alcohol and allyl aldehyde helped to identify the structure of the adsorption products of these two molecules on the surface. The presence of the related C 1s feature of C=C for allyl alcohol and allyl aldehyde, and the absence of C 1s feature of C=O for allyl aldehyde provided strong evidence to support that [2+2] C=C cycloaddition does not occur in the presence of hydroxyl or carbonyl groups. Furthermore, by comparing the experimental results and the adsorption energies of the adstructures calculated by DFT, it was concluded that these molecules do not react with the Si dimers through both of their functional groups, while the reaction of only one of the two functional groups is preferred on the surface. Formation of ethylene, acetylene, and propene from allyl alcohol and allyl aldehyde, simultaneously to CO from allyl alcohol, was concluded from the corresponding TPD results, which also confirm the structure of the adsorbates on the surface. The present research shows that reactions involving oxygen-containing functional groups are favoured over the other plausible reactions including [2+2] C=C cycloaddition on the Si(100)2×1. The preference of the surface to react with one of the two functional groups calls for future studies for the selective functionalization of Si(100)2×1 with potential applications in molecular electronics.

In this thesis, we compared electrical performance and stability of a novel nanocrystalline Si (nc-Si) thin film phototransistor (TFT) phototransistor and a regular amorphous silicon (a-Si:H) TFT phototransistor for large area imaging applications. The electrical performance parameters of nc-Si TFT phototransistor were extracted from the electrical (current-voltage) testing in dark and under illumination. The field-effect mobility is found to be around 1.2 cm2V-1s-1, the threshold voltage around 3.9V and the sub-threshold voltage slope around 0.47V/Dec. Optical properties of nc-Si TFT phototransistor have been evaluated under the green light illumination in the range of 1014 – 1017 lum, and the photocurrent gain and the external quantum efficiency were extracted from the experimental results. By comparing the results with those for a-Si:H TFTs measured under the same conditions, we found that nc-Si TFT has higher photo current gain under low illumination intensity, 5 ×1014 to 7 ×1015 lum. This thesis shows the relations bewteen the photo current gain, the external quantum efficiency, TFT drain and TFT gate bias; the photo current gain and the external quantum efficiency can be controlled by the Vds and the Vgs.

The dissociative adsorption of three carboxylic acids (acetic acid, propanoic acid, and acrylic acid), allyl alcohol, and allyl aldehyde on Si(100)2×1 at room temperature has been investigated by X-ray photoelectron spectroscopy (XPS) and temperature programmed desorption (TPD), as well as density-functional theory (DFT) calculations. The C 1s features obtained by XPS measurement for acetic acid, propanoic acid, and acrylic acid show that formation of bidentate carboxylate at a low exposure is followed by that of unidentate carboxylate at a higher exposure, with approximately equal population for both adstructures. The signatures of C 1s features attributed to methyl (285.7 eV), ethyl (285.3 eV), ethenyl (285.0 eV), and bidentate carboxyl (286.8 eV) and unidentate carboxyl (289.8-289.3 eV) carbons were observed for the studied carboxylic acids. The results showed that the carboxyl group is more reactive than the alkyl or alkenyl group towards the Si(100)2×1 surface, with O−H dissociation preferred over [2+2] C=C cycloaddition and the other plausible reaction products. This was also supported by our DFT calculation which showed that the bidentate carboxylate adstructure is the most stable configuration among the calculated adstructures for the aforementioned carboxylic acids. The combined temperature-dependent XPS and TPD studies provided strong evidence for the formation of ketene, acetaldehyde and CO from acetic acid, CO and ethylene from propanoic acid, and CO, ethylene, acetylene, and propene from acrylic acid. Furthermore, the TPD results provided further evidence for the preferred structure of the adsorbate from each of the carboxylic acid on the surface. In addition to carboxyl group, reactivity of the hydroxyl and carbonyl functional groups relative to that of ethenyl group was studied by investigating the reaction of allyl alcohol and allyl aldehyde on Si(100)2×1 at room temperature. The C 1s XPS results supported O−H dissociation for allyl alcohol and [2+2] C=O cycloaddition for allyl aldehyde over the [2+2] C=C cycloaddition. The similarity between the observed C 1s features for allyl alcohol and allyl aldehyde helped to identify the structure of the adsorption products of these two molecules on the surface. The presence of the related C 1s feature of C=C for allyl alcohol and allyl aldehyde, and the absence of C 1s feature of C=O for allyl aldehyde provided strong evidence to support that [2+2] C=C cycloaddition does not occur in the presence of hydroxyl or carbonyl groups. Furthermore, by comparing the experimental results and the adsorption energies of the adstructures calculated by DFT, it was concluded that these molecules do not react with the Si dimers through both of their functional groups, while the reaction of only one of the two functional groups is preferred on the surface. Formation of ethylene, acetylene, and propene from allyl alcohol and allyl aldehyde, simultaneously to CO from allyl alcohol, was concluded from the corresponding TPD results, which also confirm the structure of the adsorbates on the surface. The present research shows that reactions involving oxygen-containing functional groups are favoured over the other plausible reactions including [2+2] C=C cycloaddition on the Si(100)2×1. The preference of the surface to react with one of the two functional groups calls for future studies for the selective functionalization of Si(100)2×1 with potential applications in molecular electronics.

In this thesis, we compared electrical performance and stability of a novel nanocrystalline Si (nc-Si) thin film phototransistor (TFT) phototransistor and a regular amorphous silicon (a-Si:H) TFT phototransistor for large area imaging applications. The electrical performance parameters of nc-Si TFT phototransistor were extracted from the electrical (current-voltage) testing in dark and under illumination. The field-effect mobility is found to be around 1.2 cm2V-1s-1, the threshold voltage around 3.9V and the sub-threshold voltage slope around 0.47V/Dec. Optical properties of nc-Si TFT phototransistor have been evaluated under the green light illumination in the range of 1014 – 1017 lum, and the photocurrent gain and the external quantum efficiency were extracted from the experimental results. By comparing the results with those for a-Si:H TFTs measured under the same conditions, we found that nc-Si TFT has higher photo current gain under low illumination intensity, 5 ×1014 to 7 ×1015 lum. This thesis shows the relations bewteen the photo current gain, the external quantum efficiency, TFT drain and TFT gate bias; the photo current gain and the external quantum efficiency can be controlled by the Vds and the Vgs.

In this thesis, we will investigate the degradation of the low temperature polycrystalline silicon TFTs (LTPS TFTS) under the electrical stress. The electrical stress is divided into two parts of ac stress and dc stress. We used ac stress and dc stress conditions to stress different TFTs respectively and investigate the influence of grain boundary in n-type TFT and p-type TFT by use of electrical analysis. On the other hand, degradation mechanism was confirmed by measured capacitance. In n-type TFT, the SLS poly-Si TFT which contains GB perpendicular to the channel direction owns the higher ability against dc stress and poorer ability against ac stress than the poly-Si TFT which does not contain GB. The physical mechanism for these results has been reasonably deduced by use of TFT device simulation tool (ISE_TCAD). In p-type TFT, the enhancement phenomenon is always observed after dc or ac stress. There are both existed a power-law between the variation of the drain current with stress time. The slope of power-law is related to the shortening speed of effective channel length. In either dc stress or ac stress, there are two effective factors. The one factors of them is the degradation of poly-Si film, and another one is the effective channel length shortening. In the competition of these two effective factors, the GB-TFT has more obvious enhancement than GB-TFT during dc stress. Nevertheless, during the ac stress the GB-TFT is without larger enhancement than NGB-TFT because of serious poly-Si film damage.

Semiconductor technology has already got into nanometer scale. As the dimension keeping scaling down, we can get more transistor in the same area, and furthermore the frequency and performance are also enhanced. But nowadays the development of the lithography technology has come to the neck, we must find another way to improve the performance of transistor. The reliability is more important in the shorter and shorter device channel. In this study, we fully discuss the electrical characteristics of the hot carrier effect at various temperature of 65nm MOSFETs under external mechanical stress. In order to strain the channel, silicon substrate is bent by applying external mechanical stress, the lattice of channel will be strained after applying uniaxial tensile stress. Therefore, we successfully improve drain current and carrier mobility of NMOS, but the hot carrier effect is more serious. In addition, we can understand the influence of hot carrier effect on strain silicon by bending silicon substrate with external mechanical stress. With the increase of curvature, substrate current goes up. We offer an explanation to verify this result. The temperature effect is also measured. The drain current and mobility increased with the temperature decreasing, but the substrate current increased with temperature increasing.

Abstract The primary objective for this study is to determine the variations of germanium (Ge) to silicon (Si) ratios in diatom shells from down core sediments off the southwestern coast of the Africa. Because Ge behaves like Si in the ocean and the major source of these two elements is rivers, Ge/Si ratios of the diatom are thus expected to record the intensity of weathering on continents. Two sediment cores (Site 1081 and 1084) were collected during the ODP Leg 175 in August, October 1997 and were analyzed for intervals between 3.1 and 1.9 Ma. Generally, the (Ge/Si)diatom ratios in this study show the similar trend with those reported from the Antarctic Ocean. The decline of Ge/Si ratios after 2.5 Ma is caused by the high opal mass accumulation rate, indicating the increasing rivers input of silica to the ocean. Relatively high Ge/Si ratios of diatom shells during warm periods shown by the depleted benthic foraminiferal £_18O values from the North and Equatorial Atlantic, suggesting a scenario of intensified chemical weathering on continent. Cold periods signified by £_18O-enriched values are associated with lower Ge/Si ratios. Very likely the reduced Ge/Si values reflect the prevailing weathering on continents was less chemical-dissolving due to the dry weather in cold stages.

Abstract The purpose of this thesis is to study the electrical characteristics of ultra-thin high-k gate oxide-semiconductor interfaces. The measured samples are Y2O3/Si¡BGd2O3/GaAs¡BGa2O3(Gd2O3)/GaAs MOS capacitors. An accurate C-V relation has been obtained consistently by using a model that includes both series and shunt parasitic resistances. Using the semiconductor parameters and the oxide parameters, an ideal C-V curve with Dit = 0 is fitted to the accurate capacitance data, and the interface state density is deduced by Terman method. After post - metallization annealing (PMA) at 425¢J, the oxide charge density, interface state density and leakage current were reduced. The results are following : (1) For Y2O3/Si MOS capacitors, we obtained a oxide charge density ~ 7.7 x 1010 cm-2, an interface state density ~ 3.6 x 1010 cm-2ev-1, and an equivalent oxide thickness ~ 52Å; (2) For Gd2O3/GaAs MOS capacitors, we obtained a oxide charge density ~ 9.8 x 1011 cm-2, an interface state density ~ 2 x 1011 cm-2ev-1, and an equivalent oxide thickness ~ 57Å; (3) For Ga2O3(Gd2O3)/GaAs MOS capacitors, we obtained a oxide charge density ~ 4.2 x 1012 cm-2, an interface state density ~ 6 x 1011 cm-2ev-1, and an equivalent oxide thickness ~ 91Å. The dielectric constants obtained from our data are smaller than the reported values. A possible explanation is that an interfacial layer formed at the oxide/semiconductor interface to reduce equivalent dielectric constant.